Rock Identifier
Fossil bivalve shell (Likely a fossilized oyster or other marine bivalve; exact genus is indeterminate from the image) — fossil
fossil

Fossil bivalve shell

Likely a fossilized oyster or other marine bivalve; exact genus is indeterminate from the image

AI-generated identification · may be incorrect

Cream to tan, flattened shell with radiating/concentric growth lines and possible mineral replacement. Original shell material is commonly calcite or aragonite; Mohs hardness about 3–4, dull to slightly silky luster, low cleavage, and specific gravity roughly 2.6–2.8.

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Physical properties

Cream to tan, flattened shell with radiating/concentric growth lines and possible mineral replacement. Original shell material is commonly calcite or aragonite; Mohs hardness about 3–4, dull to slightly silky luster, low cleavage, and specific gravity roughly 2.6–2.8.

Formation & geological history

Formed as a marine mollusk shell, then buried in sediment and partially mineralized or preserved during diagenesis. Age cannot be determined visually; comparable specimens range from Paleozoic to Recent fossil-bearing strata.

Uses & applications

Primarily a teaching, display, and collecting specimen; fossil shell material may also be polished for décor, but it has little industrial value.

Geological facts

The growth bands record episodic shell growth and environmental changes. Oyster-like fossils commonly preserve irregular, thickened shells adapted to attachment on seafloors.

Field identification & locations

Look for bilateral shell symmetry, a hinge or beak, layered growth lines, and sediment infill; acid fizz would support carbonate composition but may damage it. Common in marine limestone and coastal sedimentary deposits worldwide.

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Unidentified carbonate-rich concretion with a possible fossil inclusion

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Likely fossil oyster shell

Fossilized bivalve shell; exact species cannot be identified from the image

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Crinoid Stem Fossil in Matrix (Phylum Echinodermata, Class Crinoidea) — fossil

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

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Fossiliferous limestone (likely a crinoidal or shell-fragment limestone) (Bioclastic limestone, composed chiefly of calcite (CaCO₃)) — sedimentary

Fossiliferous limestone (likely a crinoidal or shell-fragment limestone)

Bioclastic limestone, composed chiefly of calcite (CaCO₃)

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Porous limestone pebble (Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image) — sedimentary

Porous limestone pebble

Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image

sedimentary
Weathered fossil bone fragment (identification uncertain) (Fossilized bone; exact taxon and mineral composition cannot be determined from the image) — fossil

Weathered fossil bone fragment (identification uncertain)

Fossilized bone; exact taxon and mineral composition cannot be determined from the image

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